Chemicals of Life


All biological organisms are made up from a series of closely related chemicals, all derived from the atoms carbon, oxygen, hydrogen and nitrogen. Indeed it is the presence of the atom carbon that distinguishes organic (living) matter from inorganic (non-living) matter. Very few inorganic materials contain carbon, whilst all organic materials do. The constituent atoms make up a series of molecules of varying sizes and complexities. Depending on the configuration of the atoms these can form proteins, fats, carbohydrates and nucleic acids. These chemical molecules form the structures of virtually all organisms. They can thus be deemed chemicals of life as these chemicals form the structures that make up living things and share great similarities, even between species. The structures that comprise the building blocks of life are cells and tissues and, even when the organism varies widely, the individual molecules that make up the cells remain essentially similar.

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This account will outline the basic structure of the building blocks of all organisms and show how important the constituent chemicals are.

Proteins as chemicals of life

Proteins are uniquely responsible for many of the functions of life (Seeley, Stephens & Tate 2003). Their structural basis comes from amino acids, which are a series of 20 molecules comprising an amino group (NH2), carboxyl group (COOH) a single hydrogen atom, and a further group of atoms of varying size and complexity (R group) attached to a carbon atom (Stryer 1988). More important than the individual structures of amino acids is the way that they can join together to form an almost infinite variety of ways. The individual amino acids form long chains that then twist and fold creating a tertiary and quaternary structure. The bonds that can then form between and within chains confer further unique properties upon the structure.

Proteins are able to act as enzymes, which are structures that affect the speed of chemical reactions within organisms. This enables processes to occur at a speed that ensures that all the reaction products such as water, oxygen or energy are available when needed. Many of these reactions take place because the enzyme provides a special surface or area where the chemicals can react. This surface or area is an appropriate shape and size due to the overall protein structure and particularly due to the temporary bonds that can form between the enzyme and reacting chemicals.

Fats as chemicals of life

Fats, or lipids as they are more correctly known, have a rather different structure to the other molecules, as they have a smaller proportion of oxygen (Goodwin 2000). This causes the overall lipid molecules to become hydrophobic (water hating); a property that is crucial in the use of lipids as the main constituent of cell membranes. The majority of cell membranes consist of a phospholipid bilayer, which is formed due to the different interactions between the lipid and the surrounding milieu, particularly in terms of water interactions.

In addition to forming cell membranes lipids, as triacylglycerols, are also used as energy stores as well as being involved in the regulation of body metabolism. Many regulatory hormones are lipid based including the steroid sex hormones as well as the prostaglandins governing the body’s response to pathogens (Seeley, Stephens & Tate 2003).

Carbohydrates as chemicals of life

One of the characteristics of living things metabolism (Seeley, Stephens & Tate 2003), invariably utilises carbohydrates as the substrate. Carbohydrates include the simple monosaccharide sugars, all with the formula (C6H12O6) and the larger but no less simple structurally, polysaccharides including starch and glycogen. These molecules all provide a significant energy store to different organisms. The simple sugars glucose, lactose and fructose traditionally form a significant part of the human diet, but the polysaccharide starch is also an important contributor to the human diet due to the fact that it is the energy store in plants (Goodwin 2000). Carbohydrates differ from proteins, lipid and nucleic acids in that their main life giving function is as energy, whether immediate or as a store.

Nucleic acids as chemicals of life

For many people deoxyribonucleic acid (DNA) is held to be the essence of life. DNA is a nucleic acid, which consists of many amino acids paired according to a common system. The structure of DNA is derived from the order and arrangement of the amino acids that make it up. The structure of DNA is known as a double helix, with the amino acids forming the rungs of the twisting ladder, and the sugar phosphate groups forming the connecting rungs.

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It is this specific arrangement of the double helix that gives rise to both the similarities and unique aspects of humans. All of the information about how to make up a human and how it should work is contained within the DNA in the cell. When sexual reproduction takes place the information from the mother and father is combined to govern how the offspring will appear, with some features coming from the mother and some the father.

Ribonucleic acid (RNA) shares many similarities to DNA but has the function of conveying the information contained within DNA in order to construct new cells. In fact RNA is essentially half of a DNA strand and has several forms, which each perform a different function related to copying the appropriate section of DNA for use in new cells or cellular maintenance.

Whilst it is not possible to explain what makes up the spark of life, it is possible to show the biological matter that forms the physical embodiment of life. Whilst all made up from the same small atoms proteins, fats, carbohydrates and nucleic acids all contribute in a unique way to the structures of life. Thus the chemical basis of these molecules can also be deemed to be the chemical basis of life itself as, without any of these molecules, life would not be able to continue.